April 28, 2013 5 Comments
The order Coleoptera (beetles) is, of course, the largest single group of animals on earth, and by most accounts the Curculionidae (weevils) and their close relatives are the largest family-level group within the order. At 60,000 species and counting, weevils account for approximately one out of every 20 described life forms, and as a result their diversity of forms, colors and life histories are as staggering as their numbers. Among the small slice of the group that I have seen, Megabaris quadriguttatus is without question the most colorful, but species in the related genus Eurhinus (both genera belong to the curculionid subfamily Bardinae, which I point out here for reasons discussed below) must rank as among the shiniest of all weevils. Twenty-three species, all colored brilliant metallic green, blue, purple or red, are known from this exclusively Neotropical genus (Vaurie 1982), one of which has also recently established in southern Florida (Ulmer et al. 2007). The individual featured in this post was seen April 2012 in northern Argentina near La Escondida (Chaco Province) and compares well with Eurhinus adonis (ID courtesy Charles O’Brien, Green Valley, AZ). Vaurie (1982) records that species from southern Brazil, Bolivia, Paraguay and Argentina (although only from Missiones Province in the latter) and says that nothing is known of its biology.
This is certainly among the most challenging insects that I’ve ever photographed. Overblown specular highlights are a constant challenge in flash macrophotography of bright, shiny, metallic beetles, and yellow flowers are prone to blown highlights as well. Add on top of that my desire for a blue sky rather than the typical black background and the usual difficulties of hand-held, field photography of an actively moving subject, and you’ve got a quadruple challenge. Adequate diffusion of the flash is critical, and although the diffusers I was using at the time weren’t perfect, they were enough in combination with intentional underexposure of the photograph to further minimize the chance of blown highlights (underexposed photographs can be relatively easily “fixed” during post-processing, as all of the information is still there, while overexposed photographs can rarely be fixed because the information is gone). Bumping up the ISO (in this case 400) also helps—higher sensitivity to light by the sensor not only allows light from the sky to register and create a blue background, but also further reduces flash duration and the risk of blown highlights. No amount of camera settings, however, can address the final challenge—getting the subject well composed and in focus within the frame. For that, the three “P”s (patience, practice, and persistence) are the only advice I can offer.
This genus of weevils was involved in one of the more interesting nomenclatural problems that I’ve encountered. The genus was originally given the name Eurhin by Illiger in 1807, but Schönherr in 1824 changed it to Eurhinus—believing (incorrectly) that Eurhin was not a properly formed name. Unfortunately, the name Eurhinus had already been used by Kirby in 1819 for a different genus of weevils in the subfamily Apioninae. The rules of zoological nomenclature, of course, prohibit the same name being used for two different genera, and several attempts were made during the following years to provide a replacement name for Schönherr’s Eurhinus. None gained acceptance, however, and eventually Schönherr in 1833—still considering justified his correction of Eurhin to Eurhinus—proposed the name Eurhynchus for Kirby’s Eurhinus. Remarkably, the name Eurhynchus also had been used previously (for a genus of birds). Nevertheless, the change gained acceptance, and both of Schönherr’s names remained in use for the next century and a half—Eurhinus in the subfamily Baridinae and Eurhynchus in the subfamily Apioninae, with both credited to Schönherr. Strict application of the rules of nomenclature would require that the name Eurhinus be transferred back to the apionine genus and credited to Kirby and the name Eurhin resurrected for the baridine genus and credited to Illiger. However, as pointed out by Zimmerman & Thompson (1983) this would not only destroy more than a century’s worth of nomenclatural stability but also complicate the formation of family-group names such as tribes—since the two original names each have the same root (Eurhin-), tribal names based on them would be identical (Eurhinini). To resolve these issues, a formal application was submitted to the International Commission of Zoological Nomenclature (ICZN) to preserve Schönherr’s long accepted usage of Eurhinus and Eurhynchus. To do this, the ICZN would not only have to declare Schönherr’s correction of Eurhin to Eurhinus justified, but also suppress the original use of the name Eurhynchus (as a genus of birds) in order to allow Schönherr’s subsequent use for the apionine genus to stand. Fortunately, suppressing the first use of Eurhynchus had no impact on stability, since an older name was already in use for the genus of birds and the younger name had not been used since its original description. The authors of the application also noted the support of several contemporary weevil specialists (including Charles O’Brien) and that Patricia Vaurie, in her revision of the genus one year earlier (Vaurie 1982), had used the original name Eurhin with reluctance on the then-correct advice of her contemporaries. It was a classic case of priority versus stability, and while the ICZN typically is rather conservative in favoring priority, they were clearly swayed in this case by the interests of stability and impact on formation of family-group names.
Ulmer, B. J., R. E. Duncan, J. Prena & J. E. Peña. 2007. A weevil, Eurhinus magnificus Gyllenhal (Insecta: Coleoptera: Curculionidae). University of Florida, IFAS Publication #EENY-417/IN751, 6 pp.
Vaurie, P. 1982. Revision of Neotropical Eurhin (Coleoptera, Curculionidae, Baridinae). American Museum Novitates 2753:1–44.
Zimmerman, E.C. & R. T. Thompson. 1983. On family group names based upon Eurhin, Eurhinus and Eurhynchus (Coleoptera). Bulletin of Zoological Nomenclature 40:45–52.
Copyright © Ted C. MacRae 2013